Connection and distinction of tumor regression grading systems of gastrointestinal cancer

As the neoadjuvant therapy has been successfully introduced in the treatment of gastrointestinal malignancies, the evaluation of therapeutic effectiveness is becoming increasingly important. Tumor-node-metastasis system has been widely applied. However, this system is mainly based on the location of residual tumor, but does not consider the amount of residual tumor. Tumor regression grading system, a quantitative method to assess the reaction of tumor to neoadjuvant treatment, could be used as a supplement to tumor-node-metastasis system and provide additional information on prognosis. To date, numerous gastrointestinal grading systems have been used in esophageal/esophagogastric junction carcinoma, gastric adenocarcinoma, colorectal cancer, and most of them were considered to associate with clinical outcomes. In this review, firstly, we expounded the importance of tumor regression grading systems, and summarized the histopathological changes after neoadjuvant therapy. Secondly, we introduced some commonly used gastrointestinal systems, as well as the relationships and nuance. Finally, we discussed pivotal issues about these systems. In this part, we explained the calculation methods based on grid points and square measures, discussed several factors leading to observer bias, containing the slice number and the grading tier number, and analyzed the factors that might affect clinical significance, covering anatomical location, the selection of survival index, and the tumor type. Tumor regression grade systems could be divided into two main classifications, the relative amount of fibrosis and residual tumor, and the proportion of residual tumor in the tumor bed. However, the definitions of these systems were still need to be improved. The tumor regression grading system is useful in evaluating tumor response to neoadjuvant therapy, but more work is needed to refine and unify the system.